[Console][PhpUnitBridge][VarDumper] Fix NO_COLOR empty value handling

Output/StreamOutput.php

@@ -91,7 +91,7 @@ protected function doWrite(string $message, bool $newline)
     protected function hasColorSupport()
     {
         // Follow https://no-color.org/
-        if (isset($_SERVER['NO_COLOR']) || false !== getenv('NO_COLOR')) {
+        if ('' !== ($_SERVER['NO_COLOR'] ?? getenv('NO_COLOR') ?: '')) {
             return false;
         }